Recovery of hydrocarbons



Dec.`8, 1953 s. F. MAGOR l-:T Al.

RECOVERY oF HYnRocARBoNs Original Filed June 25, 19.48

ATTOE NEW Patented Dec. 8, i953 RECOVERY oF njYDRoCARBoNs Y Stuart F.Magor and Robert A, Daugherty, Houston, Tex., assignors to The SuperiorlOil Company, Los Angeles, Calif., a corporation of California fcontinuation of application sei-iai No. 35,146,

June 25,1948. This application December 29,

1951, Serial N0. 264,138 l 2 Claims. (Cl. 'ISG-8) The invention relatesto va process and a plant for the recovery of hydrocarbons from highpressure well fluids and in particular to a process and anabsorptionplant wherein the absorbing oil used in the plant to recoverhydrocarbons from the well fluid, and the well fluid are cooled prior tocontact whereby a light absorbing `i1 may be used in such process.

lThis application is a continuation of my prior co-pending applicationfiled on June 25, 1948, bearing Ser. No. 35,146, now abandoned, for anlinvention in Recovery of Hydrocarbons. The present application isentitled to the benet of the filing date of said earlier led applicationfor all common subject matter.

Heretofore, in the recovery of hydrocarbons from well fluids it has beencustomary to subject the well fluid to a high pressure absorption inwhich a relatively heavy absorbing oil is used to denude the Well fluidof the soluble hydro'- carbons therein. Of course the type oil used inthe absorption system depends upon the operating pressure oftheabsorption system, the temperature'at which the absorption tower isoperated and other such features.

` For example, with pressures up to 300 lbs. per

. sq. inch-gauge itis" customary to use an oil of 40 'degrees to 42degrees API with minimum molecular Weight of about 160. This oil has onan average about .0427 pound mol. per gallon and is considered in theart as being a light oil.

With pressures up to 700 lbs. per square inch gauge it iscommon to usean absorbing oil of about 36'API with an average molecular weight ofabout 190. This oil will have an average of .0370 mol per gallon. Atpressures from 1000 to 1500 lbs. per square inch gauge or higher. it iscommon to use anabsorbing oil of about 32 degrees API with a molecularweight of approximately 230 to 260. The average number of mols pergallon of this oil will be about .0314; this oil is much heavier thanthe 40 degree oil and is considered a heavy oil in the art.

Since the absorption of the hydrocarbons from the well fluid is basedupon the number of mols of absorbingoil circulated through theabsorption system it seems obvious from the foregoing illustration thata light oil of about 40 to 42 degrees API is 1.36 times as effective asthe heavy or 32 degree API oil whenr based on a gallonage basis.

It has heretofore been customary to operate such systems atapproximately 90 degrees F. and at high pressures (for example from 700pounds per square inch). to use a heavy absorbing oil having an averagemol Weight of about 230 to 260.

It is necessary to use this type oil at the tern-V peratureaforementioned at pressures ranging vfrom '700 lbs. per square inch onup, since the absorbing oil is subject to retrograde vaporisa-A pass outof the absorptionr systemwalong with the denuded well fluid.

It seems obvious from the foregoing that if a lighter oil could besubstituted for the heavier oil in the absorption systemwithout'sufiering any greater loss thereof by retrograde vaporization agreat number of benets would be derived. For example, a smaller amountof absorbing oil could be circulated through the system, while stillobtaining a highly eiiicient denuding of the wellv fluid and since theoil Would be lighter the pumping costs would be reduced accordingly ascompared to when heavy oil is used in the absorption system.Furthermore, it would be more economical to separate a light absorbingoil from the absorbed constituents.

It is an object therefore of the present invention to provide a methodof treating well uid to recover hydrocarbons therefrom by the use of'alight absorbing oil or menstruum.

Another object of the invention is to enable adjustment of temperatureof incoming well uid which is to be subjected to an absorption processand the absorbing oil used in such process in a manner that a lighteroil may be used as the absorbing oil.

It is still another` object of the invention to dehydrate the Well iiuidprior to subjecting it to an absorption system whereby formation ofhydrocarbon hydrates is eliminated and corrosion of the absorptionsystem is minimized.

Yet another object of the invention is to provide a process forstripping selected hydrocarbons from a well fluid in an absorptionsystem, the absorbingoil in such system being a light oil but thetemperature of such system being maintained at a point to inhibit lossof such absorbing oil by retrograde vaporization.

Another object of the invention is to use a light oil in an absorptionsystem to recover desired hydrocarbons from a high pressure well iluidand to thereafter selectively remove such hydrocarbons from theabsorbing oil.

Another object of the invention is to use a light oil in anabsorptionsystem to recover desired hydrocarbonsfrom a high pressure well fluidhaving an end point of approximately 225 F.

and then subjecting the bottom product comprising the remaining absorbedhydrocarbons and absorbing oil to dry distillatonin-a low pressurestill, resulting in a completely dehydrated absorbing oil.

A still further object is to provide a method and apparatus for recoveryof hydrocarbons by absorption and in a manner that upon comple-f:`

tion of the recovery operation the absorbing oil reclaimed for reuse issubstantially denuded of water.

Other and further objects and advantages of the invention will becomemore readilyapparent from a consideration of the accompanying drawingwhich is a schematic diagram of a flow sheet illustrating the preferredembodiment of theri'nvention.

In the method of operation of the plant in accordance with theinvention, high pressure well fluid from an outlet well of asubterranean formation Yis passed into the dehydration unit 2.' Thepressure of the well fluid obtained from the formation may vary from afew hundred pounds per sq. in. up to four or ve thousand pounds. It istherefore desirable to reduce and regulate the pressure of the Wellfluid before treating itin accordance with the present invention.

As a practical matterthe well fluid will probably have an initialpressure of at least '790 pounds when injected into the system, with themaximum operating pressures ranging up to which the temperature thereofis reduced to ap- V proximately 60 degrees F. This refrigeration systemmay be of any conventional type and any conventional refrigeratingmedium may be used. It is assumed of course that any distillatein thewell fluid as it comes from the formation will be subjected to adehydration processas is the gas or wel-l duid and isl then chilledalong with'the gas or well fluid in the chiller 4. An accumulator 5receives the gas distillate mixture from the Chiller 4 and the gaseousportion, or well uid, isseparated from the liquid or distillata Thegaseous portion of the well uid, denoted herein as well fluid, passes tothe high pressure absorption system denoted generally by the numeral?.

One or more absorption towers may be used which the line v9 and into thetop of the tower atlll.V

Before passing the oil into the absorption system it is passed throughthe chiller I3 which reduces the temperatures thereof to a suitablepoint so that little or no retrograde vaporization will occur attheoperating pressure ofthe absorption fsystein.l As a practical matter thepressure in the high pressure absorption system as previously statedwill range from about 700 to 2000 p. s. i.

`vlt has been determined that at about 1500 p. s. i.

it is desirableto cool the absorbing oil to a temperature approximating60 degrees F. Due to the temperature of the absorbing oil and the wellfluid prior to contact in the high pressure absorption lsystem theretrograde vaporization of the oil is limited to that which would besuffered b y aheavy cil at normally used temperature. Furthermore, it ispossible to use a lighter oil 'such Aas one having an average molecularweight of about 155 and a gravity of about 49 degrees API. A furtheradvantage resides in the fact that the cost of separation of a light oilfrom the absorbed hydrocarbons is far less than with a heavy oil.

. r'heroil from the base of the absorption system l is passed 'into theilash chamber I4 which operates at approximately 425 p. s. i. g. Theflash vapors from the flash chamber I4 are introduced into'the highpressure reabsorber I7 into which the chilled absorbing `oil injected ati8. The medium which does not vaporize in the flash chamber I4 is an oil`which is rich in the hydrocarbons absorbed from the Well uid. Thisorichoil is passed through the line I9 and is cci-mingled with the oilpassing through the line 2l)l out of the high pressure reabsorber andisthen injected into the nash chamber. 22 which operates at a pressureapproximating 200 p. s. i. g. Any vapors from this flash chamberarepassed through the line 23 and aretreated in the low pressureabsorber 2o4whioh operates at a pressure approximating500 pr. s. i. g.Absorbing oil'from the system is passed through the chiller 25 and intothe low pressure reabsorber as at 26. Ifhatpportion of the mixture ofabsorbing oil and dissolved hydrocarbons which did not vaporize in thechamber 22y is passed through theline 21 and into a heater 28 to elevatethetemperature thereof to approximately 390? F. The rich oil from-thebase of the low pressure reabsorber is also passed to the heater orpreheater 28 through the line 29. The still 30 may be operated at anysuitable pressure and temperature dependingy upon what range ofcomponents are to be extracted from the mixture of absorbing oil andhydrocarbonsjat this particular point.` For examplefitwill be assumedthat the pressure of the still 30 will be approximately 150 p. s. i-. g.Any suitable inert gas may beinjected into the still 30 and-it will beassumed that steamris injected through the line 3l so as to removehydrocarbons dissolved in the absorbing oil which vaporize up to 225degrees F. 'I'he inert gas injected inthe line 3| and the absorbedhydrocarbonspassvfrom the top of the still 30 through the line. 32 andinto the condenser 33, the components pass to the accumulator 34. A line35 from the accumulator 34 may be used to reinject aV por-tionv oftheconstituent back into the still 35 if it isV desired to maintain areflux. The residual mixtureof absorbing oil and dissolvedhydrocarbons,Y therein which were'not stripped by the inert gas streampass from the base of the tower` through the line 36 and intol thelowfpressure still 38; f

While the invention, as disclosed herein, proposes theguseo drydistillation vto dehydrate and vabsorbing oil in liquid bottoms.

denude the absorbing oil, if any, residual absorbed components. anymethod well known in the art could be used to dehydrate and denude theoil.

Heat may be applied to the still to vaporize the hydrocarbonconstituents while leaving the Of course the temperature in the still 38will depend somewhat upon the type absorbing oil used and it has beenfound that operating a plant at the foregoing pressures and with anabsorbing oil having the characteristics of that disclosed herein atemperature approximating 400 degrees is necessary in the low pressurestill to effect separation of the residual hydrocarbons dissolved in theabsorbing oil. At any event, a temperature is used in the dry stillwhich will not crack the oil. Heretofore, it has been impracticable tofinally separate the dissolved hydrocarbons from the absorbing oil by adry distillation process. However, in the present invention due to thetype absorbing oil which may be used when it and the well fluid are at asuitable temperature prior to contact with each other a dry distillationcan be used to effect separation.

The hydrocarbon components are passed out of the top of the tower 38through the line 39 and into the condenser 40. From theV accumulator 4Ithe hydrocarbon components are passed through the line 42 and into theaccumulator 34.

From here the hydrocarbon components are passed through the line 45 tosuitable fractionating means whereby they may be separated.

The absorbing oil from the still 38 is passed through the line 41 anddivided into two parts which are passed through each of the exchangers49 and 50 and into coolers 5I and 52, then to the chillers 25 and I3respectively. It is to be noted that the mixture of absorbing oil andhydrocarbons which is relatively cool as it leaves the absorption systemis passed through the heat exchangers 43 and 50 whereby the mixture ofoil and hydrocarbons obtains heat from the absorbing oil ejected fromthe still 38. Similarly the absorbing oil is cooled by the cool mixtureof absorbing oil and hydrocarbons prior to passing such oil to the oilcooler and chiller.

While specific temperatures and pressurespressures are merely exemplaryand not to serve as a limitation upon the scope of the invention.

The absorption system may be operated at any desired pressure and thewell fluid and absorbing oil may be cooled to any desired temperature;however, it is to be noted that the desired temperature of the oil andwell iluid should be one which is economically easy to obtain on the onehand, while on the other hand the temperatures should-be such so that alight oil may be used in the absorption system without sufferingsubstantial loss thereof by retrograde vaporization.

The invention is particularly adapted to high pressure absorptionsystems. The gases or well fluids from which the hydrocarbon componentsare removed are ejected out of each of the absorbers 1, l1, and 24through the lines 60, 6I, and 62 respectively. Such gas may bereinjected in an inlet well leading to the formation from which the gaswas taken or it may be directed to commerce. It is to be further notedthat by using a light absorbing oil and by dehydrating the gas prior toabsorption thereof by the absorbing oil corrosion of the equipment islessened 6 i and the ease of separation of the absorbing oil from thedissolved hydrocarbons is increased.

While the invention has been disclosed as pertaining to an absorbingoil, it is to be noted that the use of this term serves only as anexample and that any other menstruum may be used in practicing theinvention.

Broadly, the invention contemplates an absorption recovery systemwherein the fluid from which components are to be recovered and theabsorbing oil used to recover such components are regulated to apredetermined temperature prior to contact in the absorption systemwhereby a lighter oil may be used in such system.

What is claimed is:

1. A process for absorption-recovery of desired hydrocarbon fractionsfrom gases, which comprises substantially completely dehydrating thegas, refrigerating the dehydrated gas to a teniperature not above aboutF., separately refrigerating a substantially completely dehydratedabsorption oil to a temperature not above about 60 F., absorbing saiddesired fractions vfrom the refrigerated gas in said dehydrated,

refrigerated absorption oil, subjecting the resultant enriched oil to arelatively high pressure distillation step in the presence of an inertgaseous stripping medium to separate the undesired hydrocarbonstherefrom, subjecting the resultant partially stripped oil to a lowpressure dry distillation step to substantially completely removetherefrom the remaining absorbed hydrocarbons and Water, at atemperature below the cracking temperature of the absorption oil, andreturning the dehydrated oil to the second-mentioned refrigeration step,said absorption oil having an A. P. I. gravity above 42 and an averagemolecular weight below about 155.

2. A process for absorption-recovery of desired hydrocarbon fractionsfrom gases, which comprises substantially completely dehydrating thegas, refrigerating the dehydrated gas to a temperature not above about60 F., separately refrigerating a substantially completelyv dehydratedabsorption oil to a temperature not above about 60 F., absorbing saiddesired fractions from the refrigerated gas in said dehydrated,refrigerated absorption oil, subjecting the resultant enriched oil to arelatively high pressure distillation step in the presence of an inertgaseous stripping medium to separate the undesired hydrocarbonstherefrom, subjecting the resultant partially stripped oil to a lowpressure dry distillation step to substantially completely removetherefrom the remaining absorbed hydrocarbons and water, at atemperature not above about 400 F., and returning the dehydrated oil tothe second-mentioned refrigeration step, said absorption oil having anA. P. I. gravity above 42 and an average molecular weight below about155.

STUART F. MAGOR.

ROBERT A. DAUGHERTY.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,297,675 Dayhui et al. Oct. 6, 1942 2,386,057 Noble Oct. 2,1945- OTHER REFERENCES Wilson, Rei-mer and Natural Gasoline Manufacture,vol. 2l, No. 6, pages 176-181, (1942).

1. A PROCESS FOR ABSORPTION-RECOVERY OF DESIRED HYDROCARBON FRACTIONSFROM GASES, WHICH COMPRISES SUBSTANTIALLY COMPLETELY DEHYDRATING THEGAS, REFRIGERATING THE DEHYDRATED GAS TO A TEMPERATURE NOT ABOVE ABOUT60* F., SEPARATELY REFRIGERATING A SUBSTANTIALLY COMPLETELY DEHYDRATEDABSORPTION OIL TO A TEMPERATURE NOT ABOVE ABOUT 60* F., ABSORBIGN SAIDDESIRED FRACTIONS FROM THE REFRIGERATED GAS IN SAID DEHYDRATEDREFRIGERATED ASBORPTION OIL, SUBJECTING THE RESULTANT ENRICHED OIL TO ARELATIVELY HIGH PRESSURE DISTILLATION STEP IN THE PRESENCE OF AN INERTGASEOUS TRIPPING MEDIUM TO SEPARATE THE UNDESIRED HYDROCARBONSTHEREFROM, SUBJECTING THE RESULTANT PARTIALLY STRIPPED OIL TO A LOWPRESSURE DRY DISTILLATION STEP TO SUBSTANTIALLY COMPLETELY REMOVETHEREFROM THE REMAINING ABSORBED HYDROCARBONS AND WATER, AT ATEMPERATURE BELOW THE CRACKING TEMPERATURE OF THE ABSORPTION OIL, ANDRETURINING THE DEHYDRATED OIL TO THE SECOND-MENTIONED REFRIGERATIONSTEP, SAID ABSORPTION OIL HAVING AN A.P.I. GRAVITY ABOVE 42* AND ANAVERAGE MOLECULAR WEIGHT BELOW ABOUT 155.